题解 | #每月各旬有多少人练题#

#使用日期格式化函数date_format()和拼接函数concat()
select concat(date_format(event_date,'%Y年%m月'),
case when day(event_date) between 1 and 9 then '上旬'
    when day(event_date) between 10 and 19 then '中旬'
    else '下旬'
    end
) as dt_range,
count(distinct device_id) as cnt
from question_practice_detail
group by 1
order by substr(dt_range,6,2) desc,2 desc